1,721,019 research outputs found
Experimental validation and characterization of mean swash zone boundary conditions
No full textPerformances of recently developed shoreline boundary conditions for wave-averaged nearshore flow solvers are evaluated on the basis of available experimental data. Applications of the model to experimental data show the chosen equations suitably determine boundary values required for one-dimensional mean flow. A detailed illustration is also given of the characteristics of flow properties which appear in the model. It is, finally, shown that very simple conditions can be suitably used at the mean shoreline of wave-averaged flows for which boundary values of position, water depth, and velocity are computed on the basis of local quantities known at the seaward boundary of the swash
Revealing the shape of turbulence in channel flows
No full textThe proposed research focuses on a novel geometric approach to study Navier- Stokes turbulence. In the last century, the study of turbulence has been ap- proached following the great Kolmogorov’s physical insights on the inertial energy cascade and, more recently, by investigating the geometry of the state space of the Navier-Stokes equations treated as a dynamical system. This novel geometric approach arises from the evidence that what is observed in physical space sometimes is not always suggestive of the hidden laws of physics of the turbulent motion. Thus, looking at the turbulent dynamics in state space may lead to a new understanding of the associated physical processes. In particular, vortices in a channel flow change shape as they are transported by the mean flow at the Taylor speed, or dynamical velocity. Removing the translational (Toric) symmetry in state space reveals that the shape-changing dynamics of vortices influences their own motion, and it induces an additional self-propulsion velocity, or geometric velocity. Thus, in strong turbulence, the Taylor’s hypothesis (Taylor, 1938) of frozen vortices is not satisfied because the geometric velocities can be significant. In my PhD work, I aim at revealing the shape of turbulence in channel flows. In particular, I study how vortices change shape as they are transported by the mean flow, and how these shape- changing dynamics influence their own motion. This study yields the discovery that the geometric velocity, induced by vortex shape changes, is the physical manifestation of hidden wave-like dispersion properties of turbulence
On using boussinesq-type equations near the shoreline: a note of caution
No full textWe briefly analyze some characteristics of the behavior in very shallow waters i.e. near the shoreline of high-order (dispersive-nonlinear) Boussinesq-type equations. By using the Carrier and Greenspan (1958) solution as test flow conditions we illustrate the behavior of both purely dispersive and dispersive-nonlinear contributions near the shoreline. It is also shown that Boussinesq-type equations can be more usefully handled in the swash zone if written in terms of the total water depth. (C) 2002 Elsevier Science Ltd. All rights reserved
A comparison of two different types of shoreline boundary conditions
No full textTwo different types of shoreline boundary conditions which can be used in either wave-resolving or wave-averaging models of waves and currents propagation in the nearshore are compared here. The two techniques are essentially different: in the first case the velocity of the shoreline is obtained by the momentum equation and the shoreline position is tracked by changing the grid position, while in the other case the velocity of the shoreline is obtained by a modified Riemann solver and the shoreline is defined as an interface between dry and wet fixed grid points. A number of test cases are described to compare the performance of the two techniques. (C) 2002 Elsevier Science B.V. All rights reserved
On the shoreline boundary conditions for Boussinesq-type models
No full textWe propose and illustrate a novel type of shoreline boundary conditions for Boussinesq-type models. On the basis of characteristic equations of the non-linear shallow water equations, boundary conditions are developed equations that can suitably model the motion of the instantaneous shoreline. Such boundary conditions are then implemented in a numerical solver for a specific set of Boussinesq-type equations, which have been proved very effective for near-shore modelling. Finally, a number of tests are performed to validate and illustrate the behaviour of the new conditions. Copyright (C) 2001 John Wiley & Sons, Ltd
Swash zone boundary conditions for long wave models
No full textIn this note, a description of swash zone boundary conditions for implementation in wave-resolving and wave-averaging long-wave models is given along with a discussion of the role of such conditions on the modelling of the entire surf zone hydromorphodynamics. (c) 2005 Elsevier B.V. All rights reserved
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